Tuesday I had the pleasure of listening to Dr. Kevin Feldheim chat with a Field Museum science writer about sharks in the monthly “A Scientist Walks Into a Bar” function at The Hideout in Chicago. His research focuses on inferring the mating system and population biology of sharks using genetic markers called microsatellites. These are repetitive parts of DNA, and they help form DNA motifs. It’s the same science used to determine paternity and to profile cancer. In other words, Dr. Feldheim is the Maury Povich of ichthyology.
He talked about parthenogenesis (“virgin birth”), a method by which a shark (and other animals) can reproduce without male sperm. As unlikely as it sounds, this is a real phenomenon, observed both in aquariums and in the wild.
How does it work? Stay with me here because I have to go a little technical. Remember that meiosis is sexual reproduction, as opposed to mitosis. In meiosis, a particular type of cell copies its chromosomes and splits into four gametes, which are cells that unite with another of the opposite sex to produce a zygote, which is a fertilized egg cell.
In females, only one of the four gametes becomes the egg cell and receives the bulk of the cell material. The other gametes that are left over become something called “polar bodies,” which typically degenerate into the body. In parthenogenesis, however, one of those polar bodies fuses with the egg cell instead of disintegrating and begins embryonic development. This is called chromosomal crossing over and it means the mother’s paternal and maternal DNA strands are exchanged so the embryo is not a clone – it has half the genetic diversity of the mother.
Most shark species are in precipitous decline around the world because of the insatiable shark fin industry. Parthenogenesis, then, seems like a great alternative to traditional mating when populations are in decline. However, if this is happening as frequently as scientists suspect, the issue is a lack of genetic diversity in shark populations. The result is essentially inbred offspring. Too many of those and you end up with King Joffrey!
If you can check out this series at The Hideout, it is totally worth it. It runs monthly on Tuesdays from 6:30 to 7:30. Tickets are $5 and supposedly available at the door, but I recommend buying them ahead of time.